Surface Treatment Effect on the Grain Size and Surface Roughness of as‐Deposited LPCVD Polysilicon Films

Abstract

In this work we report on the effect of the substrate treatment on the grain size and the surface roughness of as‐deposited polycrystalline silicon films obtained by low pressure chemical vapor deposition. Deposition of silicon films was performed at 570°C on oxidized silicon substrates which were subjected to different wet surface treatments. We found that the grain size of the as‐deposited polysilicon films was significantly enhanced for films deposited on freshly oxidized silicon wafers, which were loaded immediately for deposition. This was attributed to the impurity‐free surface of the substrate, resulting in a lower nuclei density and subsequently in the development of a larger grain size. The surface roughness of these films, however, was found to be significantly higher than that of films deposited on substrates subjected to a wet surface treatment prior to deposition. The roughness was found to correlate well with the mechanism which predominantly determines the growth of the stable nuclei. When direct impingement of atoms on the nuclei predominates, a wave‐like surface develops while when lateral growth dominates, a smooth surface develops. We found that a smooth surface can be achieved either by subjecting the substrate in a wet surface treatment prior to deposition, which effectively decreases the surface diffusion length of the silicon adatoms and thus increases the density of the initial stable nuclei, or by suitably decreasing the deposition rate at a given temperature in the case of untreated substrates.